Calculations of carrier localization inInxGa1−xN

The electronic structures of cubic InGaN systems are calculated using an atomistic empirical pseudopotential method. Two extreme cases are studied. One is a pure InN quantum dot embedded in a pure GaN matrix, another is a pure ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ alloy without clustering. We find hole localizations in both cases. The hole wave function starts to be localized as soon as a few In atoms segregate to form a small cluster, while the electron wave function only becomes localized after the number of In atoms in the quantum dot becomes larger than 200. The hole state is also strongly localized in a pure ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ alloy, on top of randomly formed (110) directioned In-N-In chains. Using one proposed model, we have calculated the hole energy fluctuation, and related that to photoluminescence linewidth. The calculated linewidth is about 100 meV, close to the experimental results. Wurtzite InGaN is also studied for optical anisotropies. We find that in both quantum dot and pure alloy, the polarization is in the $\mathrm{xy}$ plane perpendicular to the c axis of the wurtzite structure.